[postgis-devel] Call for 1.4.2 and 1.5.1 (Handling of Invalid Geometries)

[Kevin Neufeld]

Interesting.  So does this mean that a 2-ordinate polygon would get converted to a LINESTRING and a 3-ordinate polygon 
would automatically have a fourth point added, thus closing the ring?

What would these clean to?
'POLYGON((0 0),(1 1 2 2))'
'POLYGON((0 0),(1 1 2 2),(3 3, 4 4, 5 5))'

-- Kevin

On 2/17/2010 1:06 PM, strk wrote:
> On Wed, Feb 17, 2010 at 11:33:22AM -0800, Kevin Neufeld wrote:
>> On 2/17/2010 10:40 AM, Paul Ramsey wrote:
>>> Better to accept invalidity in
>>> all its flavors and provide the tools to identify and work on
>>> improving it inside the database.
>>
>> I'm torn.  I totally agree that PostGIS needs to accept invalid geometries
>> for all the reasons Chris and Paul gave.  But I'm kinda with Mark on this
>> one - there is a difference between geometry invalidity and what
>> constitutes a geometry in the first place.  Shouldn't a POLYGON at least
>> look something like a POLYGON before being allowed into PostGIS? Obviously
>> in this case, it makes most sense to automatically add any missing
>> closing-ring points.  But what if the polygon only has one point (ie.
>> 'POLYGON((0 1))')?
>
> I just committed handling of this by ST_MakeClean:
>
> # select st_astext(g) as orig,
> 	 st_isvalidreason(g) as invalidity,
> 	 st_astext(st_makevalid(g)) as valid
> from (
> select '0103000000010000000100000000000000000000000000000000000000'::geometry
> as g) as foo;
> -[ RECORD 1 ]-------------------------------------------------------------------
> orig       | POLYGON((0 0))
> invalidity | IllegalArgumentException: point array must contain 0 or>1 elements
>             :
> valid      | POINT(0 0)
>
> Get these dirty things in, DBs shouldn't be picky.
> We have already st_isvalid() for use to check state !
>
> --strk;
>
>    ()   Free GIS&  Flash consultant/developer
>    /\   http://foo.keybit.net/~strk/services.html
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